Energy assisted magnetic recording (EAMR) or heat assisted magnetic recording (HAMR) technology is often used to increase areal density of information storage devices such as magnetic disks. In these assisted recording systems, a laser beam is delivered through an optical waveguide and interacts with a near field transducer (NFT) that absorbs part of the optical energy and forms a very strong localized electromagnetic field in the near field region. When the localized electromagnetic field is close enough to the recording medium, the recording medium absorbs part of the localized electromagnetic field energy and heats up thermally, which helps to realize the whole magnetic recording process.
A primary design goal of EAMR involves getting high media absorption efficiency. Media absorption efficiency is defined as energy being absorbed by media layers divided by incident light energy in the optical waveguide. A key challenge to improving media absorption efficiency is to find a waveguide structure that provides strong interactions between the waveguide mode and the near field transducer (NFT). The stronger the interactions between these components, the stronger the electrical field produced by NFT will be. Therefore, given the strong interactions between the waveguide mode and the NFT, the media absorption efficiency will be larger.
A number of different light delivery designs have been proposed in an attempt to maximize NFT efficiency. One such design uses a planar waveguide with a parabolic solid immersion mirror to focus laser light on a disk-shaped NFT. The key to realizing this structure is to properly introduce a pi phase shift between the light waves coming to the NFT from the opposite sides of the parabolic mirror.
Another design uses a channel waveguide to deliver light to an aperture based NFT. The light is coupled into the optical channel waveguide via a mode converter and is guided to the vicinity of the NFT. At the air bearing surface (ABS) side, the light interacts with an NFT and forms a very strong localized electrical field.
However, the above described designs provide weak interaction between incident light and the NFT resulting in low media absorption efficiency. In addition, these designs impose some challenges to the EAMR manufacturing processes due to tight process tolerances. As such, an improved waveguide structure for increasing media absorption efficiency without negatively impacting current optical waveguide manufacturing processes is needed.